This invention relates to an optical information recording card using a polymer blend that exhibits phase separation by heating as the recording material in which information can be written by a semiconductor laser beam.
With the rapid advance of semiconductor lasers in recent years, remarkable development has been achieved in optical memories which are advantageous over magnetic memories in the capability of very high density recording and also in excellence of durability by reason of noncontact recording and reproducing. For civil uses, optical disc memories of ROM type recorded with audio and/or video signals have already been commercialized by the names of compact disc, laser disc and optical disc. Besides, writable but inerasable optical disc memories of the so-called WORM (write once read mostly) type have been developed and are in practical use in some offices and public institutions.
Also efforts have been devoted to application of the technology of optical memories to plastic cards represented by credit cards and bank cards for enhancement of recording density and augmentation of recording capacity. In the conventional information recording cards using embossed characters or magnetic stripes for recording, recording capacity does not always suffice for needs. One way of enlarging the recording capacity is embedding an IC in the card. Actually, so-called IC cards having recording capacity of 16 KB are nearing to practical use. However, recording capacity of plastic cards can be further enlarged by utilizing an optical recording technique. In laboratories, optical information recording cards of ROM type larger than 200 KB in recording capacity have already been produced. Besides very high recording density, lowness of recording cost per bit will become an important merit of optical information recording cards. Rewritable optical information recording cards and WORM type optical information recording cards are also under development.
Known optical recording materials include colloidal organic materials in which silver particles are dispersed and metal salts for precipitation of metal particles by a sort of electroless plating process. In the case of using a semiconductor laser beam for recording of information, the laser beam is focussed to a very small spot on the surface of an optical recording layer and is guided so as to one-dimensionally write information into the recording layer. In such a case the material of the recording layer is usually an alloy or intermetallic compound which is fundamentally composed of Al, Te, Bi, Se, Sn, Tb, Co, Fe and/or In. Besides, there are proposals for use of organic pigments of cyanine type.
As to the above mentioned metallic recording material, a disadvantage is that most of the essential metals have toxicity and, hence, have to be handled with great care. This becomes a particularly serious matter of concern in the cases of information recording cards with which human bodies very frequently make direct contact. Besides, the metallic material is susceptible to oxidation or some corrosion and do not possess good storability. At present these shortcomings are coped with by providing a protective film on the recording layer. Nevertheless, the recording layer gradually deteriorates by oxidation or partial corrosion and consequently becomes low in recording sensitivity and/or reading sensitivity. Optical recording materials using organic pigments still involve various problems including insufficient stability and durability.
Meanwhile, U.S. Pat. No. 4,617,350 discloses a thermoplastic resin composition which is essentially a blend of an acrylic ester polymer and a copolymer of vinylidene fluoride and hexafluoropropane and which exhibits phase separation by heating and serves as a thermochromic material. Japanese patent application No. 61-27910 proposes an optical information recording card using a polymer blend of the type disclosed in U.S. Pat. No. 4,617,350 as the recording material in which information can be written by a semiconductor laser beam. This optical recording material is free from deterioration by oxidation or corrosion. However, this recording material is rather low in light absorbing efficiency in the wavelength range of semiconductor lasers and, hence, is insufficient in recording sensitivity.